The continuing magnitude of breast cancer with respect to incidence and mortality and the limited options for treatment provide a strong rationale for identifying new, selective molecular targets for prevention of this malignancy. Recently, cyclooxygenase-2 (COX-2) and peroxisome proliferator-activated receptors-y (PPARgamma) have been characterized as holding great promise for breast cancer chemoprevention. Both molecules regulate important biological processes and may play a role in breast carcinogenesis. Induction of COX-2 and inactivation of PPARgamma occur in this malignant disease and it appears that they contribute to cancer induction either directly or via their coordinate effects on a wide array of cancer-related genes and transcription factors. Our studies and those of others indicate that inhibition of COX-2 or activation of PPARY prevents mammary carcinomas in rodents. Combinational chemoprevention, whereby synergism can be achieved between two drugs, represents an important advancement in the field of cancer prevention. Our preliminary observation indicates that targeting COX-2 and PPARgamma can synergistically inhibit the proliferation of human breast cancer cells. Taken together, we hypothesize that simultaneous targeting of COX-2 and PPARy may inhibit the development of mammary gland carcinoma to an extent superior to that produced by targeting either of these two regulatory molecules alone. Further, we believe that COX-2 inhibitors and PPARy-agonists may act via a common pathway(s) or mechanism(s) of action through which they influence the expression of a wide array of genes and transcription factors and, thereby, elicit their cancer preventive effects. To test our hypothesis, we plan to accomplish the following specific aims: Aim 1: to determine the chemopreventive efficacy of a COX-2 selective inhibitor (celecoxib) and a PPARy-agonist (rosiglitazone) when administered in combination on the N-methyl-N-nitrosourea-induced rat mammary gland carcinogenesis during initiation and post-initiation stages. Aim 2: to elucidate the mechanistic action of celecoxib and rosiglitazone on chemoprevention by identifying target genes and transcription factors modulated in the mammary epithelial cells of rats treated with both agents at various time intervals, using CDNA microarray analyses. This pilot preclinical study introduces a novel strategy for breast cancer prevention. Results of this study may enable us to: i) deten-nine the significance of simultaneous targeting of COX-2 and PPARgamma, ii) identify mechanisms by which COX-2 inhibitors and PPARy-ligands elicit their cancer preventive effects, and iii) evaluate the applicability of this approach of the prevention of human breast cancer.